Shrinky Dink® Stuffed Animal Goggles

I have previously blogged (see: http://campbelldemo.blogspot.com/2012/05/homemade-shrinky-dinks.html) about how transparent polystyrene packaging such as those used to hold baked goods can be used to make plastic trinkets, and how this polymer behavior is the basis for Shrinky Dinks®, a craft/toy that was popular in the 1970s and 1980s, and can still be purchased today (®Shrinky Dinks is the Registered Trademark of K & B Innovations, Inc.).  I have found that if you trace a pair of lab goggles onto a sufficiently large piece of polystyrene packaging, cut it out, punch a hole at either side, and shrink it in a toaster oven, the resulting goggle shape is a size that fits stuffed animals. I used an elastic band to hold the "goggles" in place.

Human Battery

In my electrochemistry lectures I point out that a person's fingers can be a salt bridge in an electrochemical cell.  In an energy exhibit at the St. Louis Science Center yesterday I saw a great demonstration of a person being an integral part of a battery.  There were two pairs of metal plates (each pair had a copper and a zinc plate connected by a wire) connected to a sensitive voltmeter.  When my hands were  placed on plates of the same metals (Cu and Cu or Zn and Zn), no electrochemical potential was established and the voltmeter read zero.  When my hands were placed on a Cu and a Zn plate that were electrically connected away from the voltmeter, the voltmeter read zero.  When my hands were placed on a Cu and a Zn plate that were electrically connected through the voltmeter, the voltmeter needle deflected as oxidation took place at the Zn plate and reduction took place at the Cu plate.  The direction of the needle deflection depended on which specific plates were touched. The magnitude of the deflection seemed to vary with the quality of the contact made with the plate (illustrating the significance of resistance in the cell).  I was reminded of a "potato clock" only this time it was a couch potato involved in the battery!  Another nice exhibit located nearby had a rod that one could gently displace to demonstrate the magnitude of a joule of energy.

pH Sensitivity of Purple Grape Juice

I have blogged before about grape juice as a dye (see: http://campbelldemo.blogspot.com/2012/05/grape-juice-prints-on-clothes.html), blackberry juice as a dye (http://campbelldemo.blogspot.com/2012/05/dyeing-seashells-with-blackberry-juice.html) and pigments in plants being sensitive to pH (http://campbelldemo.blogspot.com/2012/05/ph-sensitivity-of-colorants-in-flower.html).

So, I think it is time to mention an effect that I have been noticing for years but saw spectacularly this morning.  Purple grape juice is red out of the bottle (or out of a frozen concentrate can), but when the juice is diluted the color shifts to blue.  I interpret this as the anthocyanin pigments changing color when the pH of the solution increases as tap water is added to the juice.  The picture shows the reddish undiluted grape juice at the left, and grape juice blue as it is diluted into water at the right.